Setting the context for cloth bake
You need to override the context. AFAIK setting area.type does not work.

Baking cloth is very similar to baking fluid or smoke.
This question has already been asked for smoke and fluid, so I will quote one of the answers here:


  Baking smoke is very similar to baking fluid, so I will quote
  brecht's answer:
  
  
    It's a bit more complicated than it could be because fluid simulating baking is only exposed as an operator. That means it expects an active
    object in the context, which is usually provided by the user interface
    that is not available in background mode.
  
  
  However, it is possible to override context manually, see the api
  docs.
  
  So for a smoke simulation:

import bpy

for scene in bpy.data.scenes:
    for object in scene.objects:
        for modifier in object.modifiers:
            if modifier.type == 'SMOKE':
                if modifier.smoke_type == 'DOMAIN':
                    override = {'scene': scene, 'active_object': object, 'point_cache': modifier.domain_settings.point_cache}
                    bpy.ops.ptcache.bake(override, bake=True)
                    break

  
  This will bake the selected cache for all domain objects in the file.


Using the simple script below which is adapted from the script in the above quote (which is in turn adapted from brecht's answer about baking fluid), you can bake the cloth cache for every object in the file which has a cloth modifier:

import bpy

for scene in bpy.data.scenes:
    for object in scene.objects:
        for modifier in object.modifiers:
            if modifier.type == 'CLOTH':
                override = {'scene': scene, 'active_object': object, 'point_cache': modifier.point_cache}
                bpy.ops.ptcache.bake(override, bake=True)
                break